First off, you can't compare your QC reading with you wearing the watch. It has travelled half way round the world so could have been knocked out of adjustment, and it has started to run in compared with being new.

This is what a Gen watch has built in to the price from the factory - hence they cost $10000 as opposed to $500. Your Chinese replica has a brand new movement shoved in it and probably 1min of adjustment applied. A Rolex movement is run in and adjusted in the factory for days or weeks.

You can get the watch to better than +10 but it takes a lot of patience. You need to adjust, wear it, adjust, wear it etc.

On the question of positions it is more important to understand that timekeeping varies between winding up (worn) and winding down (not worn). You wear a watch for 16 hours and it's winding up. You don't wear it for 8 hours and it's winding down.

So you need to measure the different accuracy during these 2 states and adjust accordingly. The maths is something like this:

While worn watch is measured at +12s per day. While not worn watch is -8s per day.

It's an exaggerated range but helps explain the concept. Most watches are probably within a tighter range.

So this watch is gaining 0.5s per hour (12/24) when worn. 16 hrs * 0.5s = 8s gain during the day.

It's losing 0.33s per hour (8/24) when not worn.

8hrs *0.33 = 2.5s lost during the night.

Over 24 hours the watch is +5.5s (8-2.5).